This invention relates to a method for measuring a surface leakage current of a sample.
The electric resistance of a sample surface (i.e., surface resistance) can be measured in a manner that a voltage is applied between a pair of electrodes (which may include a combination of a central circular electrode and a ring electrode surrounding it) on the sample surface and then a current, which flows between these electrodes, is measured.
In such measurement of the sample surface resistance, if there are adhered substances on the sample surface, a leakage current caused by the adhered substances is disadvantageously to be measured as included in the total current. The leakage current caused by the adhered substances becomes error in measuring accurately an essential current flowing through the sample per se. Accordingly, cleaning of the sample surface is required in measuring accurately the sample surface resistance. The cleaning method may be performed by using cleaning solution or heating in a vacuum vessel to eliminate the adhered substances.
In cleaning the sample surface prior to the measurement, an operator might be concerned about if the adhered substances have been removed at all. That is, when the surface resistance is measured after the cleaning of a sample, an operator might be concerned about if the measurement result is for the ideal condition in which the adhered substances have been removed at all. If the operator wants, before measurement of the surface resistance, to confirm reliably if the adhered substances have been removed at all, suitable testing facilities and testing operation are required.
The measurement technique for the surface leakage current of a sample is not restricted to the above-mentioned sample surface resistance measurement but can be used in various situations. For example, in a TSC (Thermally Stimulated Current) method in which a current flowing through a sample is measured as the sample temperature varies, the adhered substances have an influence on the TSC measurement which measures a current flowing through the surface of a sample. Therefore, in such a TSC measurement, it is necessary to measure the surface leakage current under the ideal condition that the adhered substances have been removed from the sample surface. Other than the TSC, similarly in measurement means such as DEA (Dielectric Analysis: thermal relaxation measurement), DLTS (Deep Level Transient Spectroscopy), ICTS (Isothermal Capacitance Transient Spectroscopy), TSIC (Thermally Stimulated Ionic Current) IV (Current-Voltage characteristic) and CV (Capacitance-Voltage characteristic), it is preferable that the surface leakage current is measured iunder the ideal condition that the adhered substances have been removed. It is noted that all of these measurement means such as TSC, DEA, DLTS, ICTS, IV and CV belong to xe2x80x9ca thermoelectric analyzer for measuring the thermoelectric property of a sample as the sample temperature variesxe2x80x9d.
It is an object of the invention to provide a method for measuring accurately a surface leakage current of a sample without separate facilities for removing the adhered substances from the sample surface beforehand.
It is another object of the invention to provide a method for measuring a surface leakage current wherein perfect elimination of the adhered substances from the sample surface can be verified.
A method of measuring a surface leakage current according to the invention has the steps of voltage application, energy rays irradiation and current measurement. The step of voltage application applies a voltage between a pair of electrodes, which are apart from each other on a sample surface, during a predetermined voltage application period of time. The step of energy rays irradiation irradiates, by energy rays, a region of the sample surface between the pair of electrodes during a predetermined irradiation period of time which is within the voltage application period of time. The energy rays may be lasers, ultraviolet rays, X-rays or an electron beam. The step of current measurement measures a current flowing between the pair of electrodes during the voltage application period of time.
With this method, the energy rays irradiation makes a surface leakage current, which is caused by adhered substances, start to flow, and when the adhered substances have been eliminated perfectly a relatively large current caused by the adhered substances disappears. Therefore, the adhered substances can be removed at the same time that the surface leakage current is measured. Furthermore, perfect elimination of the adhered substances can be verified by confirming that a relatively large current has disappeared. This method of measuring a surface leakage current can be performed with the use of xe2x80x9ca thermoelectric analyzer for measuring the thermoelectric property of a sample as the sample temperature variesxe2x80x9d. In that case, if the surface leakage current is measured prior to the measurement of the thermoelectricity of a sample, adhered substances can be removed from the sample surface; besides, perfect elimination of the adhered substances can be verified.
With this invention, the adhered substances can be removed without separate facilities for removing the adhered substances from the sample surface beforehand but with the use of the measurement device for the surface leakage current as it is. Besides, perfect elimination of the adhered substances can be verified electrically.